Greatwall kinase (GWL) is a critical regulator of mitosis and meiosis. It regulates PP2A-B55 activity by phosphorylating two proteins, Arpp19 and ENSA. This phosphorylation turns these proteins into potent inhibitors of PP2A-B55, thereby promoting a correct timing and progression of mitosis. When over-expressed in breast cancer, GWL induces oncogenic...